Despite its significant role in the water cycle, the interaction between snowmelt and groundwater remains incompletely understood. Furthermore, climate change is altering this connectivity, a process further complicated in the Arctic by permafrost degradation. In this study, we analyze samples of snowpack, river runoff, precipitation, and groundwater collected during the warm season of 2024 in the small, unglacierized Fuglebekken catchment in Spitsbergen. These samples are examined for 17O, 18O and 2H, along with hydrochemical elements. Combined with energy-balance modeling, this approach is used to trace snowmelt from snowpack evolution to river runoff and groundwater recharge. The results show abrupt shifts in river runoff sources arising from seasonal changes in hydrological connectivity with groundwater. Dynamics of slope in the δ2H-δ18O relationship indicates strong fractionation processes in snow cover most likely connected with sublimation.